Lithium ion battery

ABSTRACT

A lithium ion battery includes at least one battery cell. The battery cell includes a cathode electrode, an anode electrode, and a separator. The separator is sandwiched between the cathode electrode and the anode electrode. At least one of the cathode electrode and the anode electrode includes a current collector. The current collector is a carbon nanotube layer consisting of a plurality of carbon nanotubes.

RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201110446801.7, filed on Dec. 28, 2011, inthe China Intellectual Property Office, the disclosure of which isincorporated herein by reference. The application is also related tocopending applications entitled, “METHOD FOR MAKING LITHIUM IONBATTERY”, filed Ser. No. 13/458,488; “LITHIUM ION BATTERY ELECTRODE”,filed Ser. No. 13/458,459; “METHOD FOR MAKING LITHIUM ION BATTERYELECTRODE”, filed Ser. No. 13/458,467; “THIN FILM LITHIUM ION BATTERY”,filed Ser. No. 13/463,042; “METHOD FOR MAKING THIN FILM LITHIUM IONBATTERY”, filed Ser. No. 13/458,502.

BACKGROUND

1. Technical Field

The present disclosure relates to lithium ion batteries.

2. Description of Related Art

A lithium ion battery includes a case, an anode, a cathode, anon-aqueous electrolyte, and a separator. The anode, cathode,non-aqueous electrolyte, and separator are encapsulated in the case. Theseparator is located between the anode and the cathode. The anode,cathode, and separator are infiltrated by the non-aqueous electrolyte.The cathode includes a cathode current collector and a cathode materiallayer disposed on a surface of the cathode current collector. The anodeincludes an anode current collector and an anode material layer disposedon a surface of the anode current collector.

The current collector is used to collect the charge generated by thelithium ion battery during discharge, and to connect to an externalpower source during the recharging of the lithium ion battery. Thecurrent collectors are usually made of metal foils, such as copper foiland aluminum foil. However, the metal foils have a relatively largeweight. The power density is calculated by power/weight. Therefore, alarge weight of the current collector will decrease the power density ofa lithium ion battery. Furthermore, the metal foils may be corroded bythe electrolyte, which decreases the life span of the lithium ionbattery.

What is needed, therefore, is to provide a lithium ion battery havinghigh power density and long life.

BRIEF DESCRIPTION OF THE DRAWING

Many aspects of the present disclosure can be better understood withreference to the following drawings. The components in the drawings arenot necessarily to scale, the emphasis instead being placed upon clearlyillustrating the principles of the present embodiments.

FIG. 1 is a schematic side view of an embodiment of a lithium ionbattery.

FIG. 2 is a scanning electron microscope (SEM) photo of an embodiment ofa drawn carbon nanotube film used in the current collector.

FIG. 3 is a schematic top view of an embodiment of a current collector.

FIG. 4 is a schematic top view of another embodiment of a currentcollector.

FIG. 5 is a structural schematic view of a lithium ion battery cathode.

FIG. 6 is an SEM image of one embodiment of a lithium ion batterycathode.

FIG. 7 is a flowchart for making a lithium ion battery according to oneembodiment.

FIG. 8 is a flowchart for making a lithium ion battery according toanother embodiment.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “another,” “an,” or “one” embodiment in this disclosure are notnecessarily to the same embodiment, and such references mean at leastone.

Referring to FIG. 1, an embodiment of a lithium ion battery 100 includesa cathode electrode 102, an anode electrode 104, a separator 106, anelectrolyte solution, and an external encapsulating shell (not shown).The cathode electrode 102, the anode electrode 104, the separator 106,and the electrolyte solution are encapsulated in the encapsulatingshell. The cathode electrode 102 and the anode electrode 104 are stackedwith each other and sandwiches the separator 106. The cathode electrode102 and the anode electrode 104 can be in contact with the separator106. The cathode electrode 102, the separator 106, and the anodeelectrode 104 form a battery cell. The lithium ion battery 100 includesat least one battery cell. If the lithium ion battery 100 includes aplurality of battery cells, the plurality of battery cells are stackedtogether. Adjacent battery cells are separated by a separator 106. Inthe embodiment according to FIG. 1, the lithium ion battery 100 includesone battery cell.

The cathode electrode 102 includes a cathode current collector 112 and acathode material layer 116 disposed on at least one surface of thecathode current collector 112. The cathode current collector 112 and thecathode material layer 116 can be two separate layers. The anodeelectrode 104 includes an anode current collector 114 and an anodematerial layer 118 disposed on at least one surface of the anode currentcollector 114. The anode current collector 114 and the anode materiallayer 118 can be two separate layers. In one embodiment, the cathodeelectrode 102 includes two cathode material layers 116 and one cathodecurrent collector 112 sandwiched between the two cathode material layers116, and the anode electrode 104 includes two anode material layers 118and one anode current collector 114 sandwiched between the two anodematerial layers 118. If the lithium ion battery 100 includes a pluralityof battery cells, in every two adjacent battery cells, the cathodematerial layer 116 in one battery cell and the anode material layer 118in the other battery cell face each other and sandwiches the separator106 therebetween.

The cathode electrode 102 can further include a conducting tab 20 (seeFIG. 3) electrically connected with the cathode current collector 112.The anode electrode 104 can further include a conducting tab 20electrically connected with the anode current collector 114. A materialof the conducting tab 20 can be metal. After the conducting tab 20electrically connects with the cathode current collector 112 or theanode current collector 114, a protecting layer can be coated onsurfaces of the conducting tab 20 to protect the conducting tab 20 frombeing corroded by the electrolyte solution. A material of the protectinglayer can be a polymer. The conducting tab 20 is configured to connectthe cathode current collector 112 or the anode current collector 114with outside.

At least one of the cathode current collector 112 and the anode currentcollector 114 is a carbon nanotube layer. In one embodiment, both thecathode current collector 112 and the anode current collector 114 arecarbon nanotube layers. The carbon nanotube layer includes a pluralityof carbon nanotubes uniformly distributed therein. The carbon nanotubesin the carbon nanotube layer can be combined with each other by van derWaals attractive force therebetween. The carbon nanotubes can bedisorderly or orderly arranged in the carbon nanotube layer. The term‘disorderly’ describes the carbon nanotubes being arranged along manydifferent directions, such that the number of carbon nanotubes arrangedalong each different direction can be almost the same (e.g. uniformlydisordered), and/or entangled with each other. The term ‘orderly’describes the carbon nanotubes being arranged in a consistentlysystematic manner, e.g., the carbon nanotubes are arranged approximatelyalong a same direction and or have two or more sections within each ofwhich the carbon nanotubes are arranged approximately along a samedirection (different sections can have different directions). The carbonnanotubes in the carbon nanotube layer can be single-walled,double-walled, or multi-walled carbon nanotubes. The thickness of thecarbon nanotube layer is not limited, and can be in a range from about0.5 nanometers to about 1 centimeter. In one embodiment, the thicknessof the carbon nanotube layer is in a range from about 1 micrometer toabout 1 millimeter. The carbon nanotube layer can include at least onecarbon nanotube film. In the carbon nanotube layer, more than one carbonnanotube film can be stacked together.

Referring to FIG. 2, in one embodiment, the carbon nanotube layer caninclude at least one drawn carbon nanotube film. The drawn carbonnanotube film includes a plurality of successive and oriented carbonnanotubes joined end-to-end by van der Waals attractive forcetherebetween. The carbon nanotubes in the carbon nanotube film can besubstantially aligned in a single direction. The drawn carbon nanotubefilm can be formed by drawing a film from a carbon nanotube array thatis capable of having a film drawn therefrom. The plurality of carbonnanotubes in the drawn carbon nanotube film are arranged substantiallyparallel to a surface of the drawn carbon nanotube film. A large numberof the carbon nanotubes in the drawn carbon nanotube film can beoriented along a preferred orientation, meaning that a large number ofthe carbon nanotubes in the drawn carbon nanotube film are arrangedsubstantially along the same direction. An end of one carbon nanotube isjoined to another end of an adjacent carbon nanotube arrangedsubstantially along the same direction, by van der Waals attractiveforce. A small number of the carbon nanotubes are randomly arranged inthe drawn carbon nanotube film, and has a small if not negligible effecton the larger number of the carbon nanotubes in the drawn carbonnanotube film arranged substantially along the same direction. The drawncarbon nanotube film is capable of forming a free-standing structure.The term “free-standing structure” includes, but is not limited to, astructure that does not have to be supported by a substrate. Forexample, a free-standing structure can sustain the weight of itself whenit is hoisted by a portion thereof without any significant damage to itsstructural integrity. So, if the drawn carbon nanotube film is placedbetween two separate supporters, a portion of the drawn carbon nanotubefilm, not in contact with the two supporters, would be suspended betweenthe two supporters and yet maintain film structural integrity. Thefree-standing structure of the drawn carbon nanotube film is realized bythe successive carbon nanotubes joined end to end by van der Waalsattractive force.

It can be appreciated that some variations can occur in the orientationof the carbon nanotubes in the drawn carbon nanotube film as can be seenin FIG. 2. Microscopically, the carbon nanotubes oriented substantiallyalong the same direction may not be perfectly aligned in a straightline, and some curve portions may exist. It can be understood that acontact between some carbon nanotubes located substantially side by sideand oriented along the same direction can not be totally excluded. Morespecifically, the drawn carbon nanotube film can include a plurality ofsuccessively oriented carbon nanotube segments joined end-to-end by vander Waals attractive force therebetween. Each carbon nanotube segmentincludes a plurality of carbon nanotubes substantially parallel to eachother, and joined by van der Waals attractive force therebetween. Thecarbon nanotube segments can vary in width, thickness, uniformity andshape. The carbon nanotubes in the drawn carbon nanotube film are alsosubstantially oriented along a preferred orientation. The drawn carbonnanotube film can be a pure structure only including the carbonnanotubes. The thickness of the drawn carbon nanotube film can be in arange from about 0.5 nanometers to about 100 micrometers. The width andlength of the drawn carbon nanotube film is not limited. When the carbonnanotube layer includes a plurality of drawn carbon nanotube films, anangle between the aligned directions of the carbon nanotubes in at leasttwo drawn carbon nanotube films can be in a range from about 0 degreesto about 90 degrees, for example can be equal to about 0 degrees, 15degrees, 45 degrees, 60 degrees, or 90 degrees.

In another embodiment, the carbon nanotube layer can include at leastone flocculated carbon nanotube film formed by a flocculating method.The flocculated carbon nanotube film can include a plurality of long,curved, disordered carbon nanotubes entangled with each other. Thelength of the carbon nanotube film can be above 10 centimeters. Thecarbon nanotubes can be randomly arranged and curved in the flocculatedcarbon nanotube film. The carbon nanotubes can be substantiallyuniformly distributed in the flocculated carbon nanotube film. Theadjacent carbon nanotubes are acted upon by the van der Waals attractiveforce therebetween, thereby forming an entangled structure withmicropores defined therein. Due to the carbon nanotubes in theflocculated carbon nanotube film being entangled with each other, theflocculated carbon nanotube film has excellent durability, and can befashioned into desired shapes with a low risk to the integrity offlocculated carbon nanotube film. The flocculated carbon nanotube filmcan be a free-standing structure due to the carbon nanotubes beingentangled and adhered together by van der Waals attractive forcetherebetween. The thickness of the flocculated carbon nanotube film canrange from about 1 micrometer to about 1 millimeter. It is alsounderstood that many of the embodiments of the carbon nanotube structureare flexible and do not require the use of a structural support tomaintain their structural integrity. The flocculated carbon nanotubefilm can be a pure carbon nanotube film only including carbon nanotubes.

In another embodiment, the carbon nanotube layer can include at leastone pressed carbon nanotube film. The pressed carbon nanotube film canbe formed by pressing a carbon nanotube array to slant the carbonnanotubes in the carbon nanotube array. The pressed carbon nanotube filmcan be a free-standing carbon nanotube film. The carbon nanotubes in thepressed carbon nanotube film are arranged along a same direction, alongmore than one predetermined different directions, or randomly arranged.The carbon nanotubes in the pressed carbon nanotube film can rest uponeach other. Adjacent carbon nanotubes are attracted to each other andcombined by van der Waals attractive force. An angle between a primaryalignment direction of the carbon nanotubes and a surface of the pressedcarbon nanotube film is about 0 degrees to approximately 15 degrees. Insome embodiment, the angle is greater than 0 degrees less than 15degrees. The greater the pressure applied, the smaller the angleobtained. The thickness of the pressed carbon nanotube film can be in arange from about 1 micrometer to about 1 millimeter. The pressed carbonnanotube film can be pure carbon nanotube film only including carbonnanotubes. The length and width of the pressed carbon nanotube filmdepend on the carbon nanotube array that is pressed. If the length andwidth of the carbon nanotube array is relatively large, the pressedcarbon nanotube film can have relatively large length and width.

If the cathode current collector 112 or the anode current collector 114is the carbon nanotube layer, the conducting tab 20 can be electricallyconnected to the carbon nanotube layer by many methods. Referring toFIG. 3, in one embodiment, the carbon nanotubes in the carbon nanotubelayer 10 are aligned along the same direction, the conducting tab 20 canhave a strip shape, and the conducting tab 20 can be arranged on thesurface of the carbon nanotube layer 10 at one side of the carbonnanotube layer 10. The conducting tab 20 can be overlapped on the sideof the carbon nanotube layer 10. The length direction of the stripshaped conducting tab 20 can be substantially perpendicular to thealigned direction of the carbon nanotubes in the carbon nanotube layer10. The carbon nanotubes have superior conductivity along the axialdirection. Therefore, in this arranged manner, the charges in the carbonnanotube layer 10 can be rapidly conducted to the conducting tab 20. Theconducting tab 20 can have a line shaped contact and connection areawith the carbon nanotube layer 10.

Referring to FIG. 4, in another embodiment, the carbon nanotubes aredisorderly arranged or intercrossed with each other in the carbonnanotube layer 10 to form a conducting network. The conducting tab 20can have a strip shape and only has an end of the strip in contact withthe carbon nanotube layer 10. The conducting tab 20 can be electricallyconnected to the carbon nanotube layer 10 through a point contact. Inone embodiment, the carbon nanotube layer 10 includes at least twostacked drawn carbon nanotube films. The carbon nanotubes in the twodrawn carbon nanotube films are substantially perpendicular to eachother. The carbon nanotubes in the two drawn carbon nanotube films canbe respectively parallel to the two perpendicular edges of the carbonnanotube layer 10. The conducting tab 20 can be arranged at the cornerof the carbon nanotube layer 10 formed by the two perpendicular edges.

The cathode material layer 116 can include cathode active material,conductive agent, and adhesive. The cathode active material can belithium manganate (LiMn₂O₄), lithium cobalt oxide (LiCoO₂), lithiumnickel oxide (LiNiO₂) or lithium iron phosphate (LiFePO₄). Theconductive agent can be acetylene black, carbon fiber or carbonnanotube. The adhesive can be polyvinylidene fluoride (PVDF) orpolytetrafluoroethylene (PTFE). A thickness of the cathode materiallayer 116 can be in a range from about 100 micrometers to about 300micrometer. In one embodiment, the thickness of the cathode materiallayer 116 is about 200 micrometers.

In another embodiment, the cathode material layer 116 consists ofcathode active material and carbon nanotubes, e.g., the cathode materiallayer 116 is free of adhesive. The cathode material layer 116 canfurther include acetylene black, carbon fiber, or any other conductiveagent. In the embodiment according to FIGS. 5 and 6, the cathodematerial layer 116 only includes cathode active material particles 14and carbon nanotubes 12. A shape of the cathode active materialparticles 14 is not limited, and can be irregular or regular. A diameterof the cathode active material particles 14 is not limited, and can beless than 15 micrometer. Referring to FIG. 5, in one embodiment, thecathode active material particles 14 can be lithium cobalt oxideparticles having a diameter less than 15 micrometer. The carbonnanotubes 12 are entangled with each other and combined by van der Waalsattractive force therebetween, thereby forming an integral continuousnet structure having a plurality of micropores defined by the carbonnanotubes 12. The plurality of cathode active material particles 14 aredispersed in the net like structure and attached on the surface of thecarbon nanotubes 12. The carbon nanotube 12 is pure, and has noimpurities adhered thereon. The carbon nanotubes 12 in the lithium ionbattery cathode 10 can serve as a conductive material and microporouscarrier to support and fix the cathode active material particles 14.Thus, even without using an adhesive, the lithium ion battery cathode 10can be an integrative stable structure due to the net structure composedof the carbon nanotubes 12. The cathode active material particles 14 areuniformly distributed in the net structure. Specifically, the cathodeactive material particles 14 can be adhered on or entangled by thecarbon nanotubes, or the cathode active material particles 14 can bewrapped by the carbon nanotubes. The cathode active material particles14 and the carbon nanotubes are in contact with each other withoutadhesive therebetween. The cathode active material particles 14 and thecarbon nanotubes are fixed together by van der Waals attractive forcetherebetween. A length of the carbon nanotubes can be longer than 200micrometer, and the carbon nanotubes can be entangled with each other toform the net structure. As such, the cathode active material particles14 can be fixed by the net structure, and the cathode material layer 116is free of adhesive.

The anode material layer 118 can include anode active material,conductive agent, and adhesive. The anode active material can be naturalgraphite, pyrolysis carbon, or mesocarbon microbeads (MCMB). Theconductive agent can be acetylene black, carbon fiber, or carbonnanotube. The adhesive can be PVDF or PTFE. A thickness of the anodematerial layer 118 can be in a range from about 50 micrometers to about200 micrometers. In one embodiment, the thickness of the anode materiallayer 118 is about 100 micrometers.

In another embodiment, the anode material layer 118 consists of anodeactive material and carbon nanotubes, e.g., the anode material layer 118is free of adhesive. The anode material layer 118 can further includeacetylene black, carbon fiber, or any other conductive agent. In oneembodiment, the anode material layer 116 only includes anode activematerial particles and carbon nanotubes. A shape of the anode activematerial particles is not limited, and can be irregular or regular. Adiameter of the anode active material particles is not limited, and canbe less than 15 micrometer. The carbon nanotubes are entangled with eachother and combined by van der Waals attractive force therebetween,thereby forming an integral continuous net structure having a pluralityof micropores defined by the carbon nanotubes. The plurality of anodeactive material particles are dispersed in the net like structure andattached on the surface of the carbon nanotubes. The anode activematerial particles are uniformly distributed in the net structure.Specifically, the anode active material particles can be adhered on orentangled by the carbon nanotubes, or the anode active materialparticles can be wrapped by the carbon nanotubes. Thus, even withoutusing adhesive, the anode material layer 118 can be an integrativestable structure due to the net structure composed of the carbonnanotubes, and the anode material layer 116 is free of adhesive.

The separator 106 can be similar to a conventional separator, such as amicroporous polymer film, a microporous ceramic film, or combinationthereof. A thickness of the separator 106 can be in a range from about 5micrometer to about 60 micrometer. In some embodiments, the thickness ofthe separator 106 is in a range from about 15 micrometer to about 40micrometer. The separator 106 includes a number of pores. A porous rateof the separator 106 can be in a range from about 20% to about 90%,diameters of the pores of the separator 106 is in a range from about 0.1micrometer to about 80 micrometer. In some embodiments, the porous rateis in a range from about 40% to 80%, diameter is in a range from about0.1 micrometer to about 10 micrometer. The electrolyte solution caninclude an electrolyte and an organic solvent. The electrolyte can belithium hexafluorophosphate (LiPF₆), lithium terafluoroborate (LiBF₄),lithium bis(oxalato)borate (LiBOB), or combinations thereof. The organicsolvent can be ethylene carbonate (EC), diethyl carbonate (DEC),dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), propylenecarbonate (PC), or combinations thereof.

The external encapsulating shell can be a rigid battery shell or a softencapsulating bag. The conductive tabs are exposed to outside of theexternal encapsulating shell, thereby connecting the external circuit.

The carbon nanotube layer used as the cathode current collector 112and/or the anode current collector 114, has relatively goodconductivity, stable chemical and electrical stability, and low weight.Therefore, the cathode current collector 112 and/or the anode currentcollector 114 can have a low weight, and the current collector does notcorrode easily, and thus has a relatively long lifespan. As such, thelithium ion battery 100 has a high power density and long lifespan.

Referring to FIG. 7, a method for making a lithium ion battery isprovided. The method includes the following steps:

S1: providing a cathode material layer and an anode material layer;

S2: forming a first carbon nanotube layer on a surface of the cathodematerial layer to obtain a cathode electrode;

S3: forming a second carbon nanotube layer on a surface of the anodematerial layer to obtain an anode electrode; and

S4: applying a separator between the cathode electrode and the anodeelectrode, thereby forming a battery cell;

S5: encapsulating at least one battery cell in an external encapsulatingshell; and

S6: injecting an electrolyte solution into the external encapsulatingshell.

In step S1, a method for making the cathode material layer is notlimited. In one embodiment, the cathode material layer is formed by thefollowing sub-steps:

S11: making a carbon nanotube source including a number of carbonnanotubes;

S12: providing a cathode active material including a number of cathodeactive material particles and a solvent;

S13: adding the carbon nanotube source and the cathode active materialinto the solvent, and shaking the solvent with the carbon nanotubesource and the cathode active material with ultrasonic waves; and

S14: separating the carbon nanotube source and the cathode activematerial from the solvent to obtain the cathode material layer.

In step S11, the carbon nanotube source can be made of carbon nanotubes.The carbon nanotubes can be single-walled carbon nanotubes,double-walled carbon nanotubes, or multi-walled carbon nanotubes. Thecarbon nanotubes can be pure, meaning there is few or no impuritiesadhered on surface of the carbon nanotubes. In some embodiments, thereare no functional groups attached on the carbon nanotubes. A length ofthe carbon nanotubes can be the same or different. The length of thecarbon nanotubes can be longer than 300 micrometers. In one embodiment,the lengths of the carbon nanotubes are substantially the same. A methodfor making the carbon nanotube source can include providing a carbonnanotube array, wherein the carbon nanotube array can be formed on asubstrate, and scratching the carbon nanotube array from the substrateto form the carbon nanotube source. The carbon nanotube source obtaineddirectly from the carbon nanotube array can make the lithium ion batterycathode stronger. In one embodiment, the carbon nanotube array is asuper aligned carbon nanotube array. A method for making the carbonnanotube array can be by CVD method, arc discharge method, aerosolmethod, or any other appropriate method.

In the step S12, the solvent can be ethanol, glycol, acetone,N-Methyl-2-pyrrolidone, water, or combination thereof. In oneembodiment, the solvent is ethanol. The solvent is contained in acontainer, such as a beaker.

In the step S13, the carbon nanotube source and the cathode activematerial form a mixture. A weight percentage of the carbon nanotubes inthe mixture can be in a range from about 0.1% to about 20%. In someembodiments, the weight percentage of the carbon nanotubes can be in arange from about 1% to about 10%. A power of the ultrasonic wave can bein a range from about 400 W to about 1500 W. In some embodiments, thepower is in a range from about 800 W to about 1000 W. A time of shakingwith the ultrasonic wave can range from about 2 minutes to about 30minutes. In some embodiments, the shaking time ranges from about 5minutes to about 10 minutes. The solvent with the carbon nanotube sourceand the cathode active material can be shaken with ultrasonic wavescontinuously or at intervals.

In step S14, after the solvent with the carbon nanotube source and thecathode active material is shaken, the carbon nanotubes in the carbonnanotube source and the cathode active material particles in the cathodeactive material combine with each other to form mixture. The mixtureconsists of the carbon nanotubes and cathode active material particles.The solvent with the mixture is kept still for about 1 minute to about20 minutes. The mixture will deposit to a bottom of the solvent. Afterthe solvent with the carbon nanotube source and the cathode activematerial is shaken, the carbon nanotubes entangled with each other toform a net structure. The cathode active material particles are wrappedby the net structure and attached on the surface of the carbon nanotubesto form an integrity mixture. The cathode active material particles havea larger density than the solvent, and as such, the integrity mixturecan be deposited to the bottom of the solvent. After the mixture hasdeposited to the bottom of the solvent, the solvent can be absorbed fromthe container by a pipe, thereby separating the mixture from thesolvent. After the carbon nanotube source and the cathode activematerial are separated from the solvent, the mixture of the carbonnanotube source and the cathode active material can be dried at a roomtemperature or at a temperature from about 25 centigrade to about 80centigrade. After the mixture is dried, the mixture can be cut directlyto form the lithium ion battery cathode. In other embodiments, themixture can be pressed and then cut to form the lithium ion batterycathode. The cathode material layer made by the above method onlyconsists of carbon nanotubes and cathode active material particles.

In step S1, a method for making the anode material layer is not limited.In one embodiment, the method for making the anode material layer isalmost the same as the method for making the cathode material layer,just using anode active material instead of cathode active material. Theanode material layer made by the above method only consists of carbonnanotubes and anode active material particles.

In step S2, the first carbon nanotube layer has the same structure withthe carbon nanotube layer disclosed above. The first carbon nanotubelayer includes at least one of the drawn carbon nanotube film, theflocculated carbon nanotube film, and/or the pressed carbon nanotubefilm. After the drawn carbon nanotube film, the flocculated carbonnanotube film, or the pressed carbon nanotube film is formed, it can belaid directly on the surface of the cathode material layer. In oneembodiment, the first carbon nanotube layer is one pressed carbonnanotube film. The first carbon nanotube film is formed on the surfaceof the cathode material layer by the following sub-steps: S21: proving acarbon nanotube array; S22: transferring the carbon nanotube array tothe surface of the cathode material layer; and S23: pressing the carbonnanotube array.

In step S21, the method for making the carbon nanotube array is notlimited. In one embodiment, the carbon nanotube array is formed on asubstrate by CVD method.

In the step S22, the carbon nanotube array is transferred on the surfaceof the cathode material layer by covering the substrate with the carbonnanotube array on the surface of the cathode material layer, wherein thecarbon nanotube array is sandwiched between the substrate and thecathode material layer.

In the step S23, a pressure can be applied on the substrate to press thecarbon nanotube array onto the surface of the cathode material layer.The substrate can be separated from the carbon nanotube array, and atleast part of carbon nanotubes in the carbon nanotube array stays on thesurface of the cathode material layer to form the first carbon nanotubelayer. The substrate can be separated from the carbon nanotube array byapplying a thin sheet between the carbon nanotube array and thesubstrate, and then removing the substrate with the carbon nanotubearray remaining on the surface of the cathode material layer to form thefirst carbon nanotube layer. After the substrate is removed, the carbonnanotube array remaining on the surface of the cathode material layercan be further pressed.

In step S3, the method of forming the second carbon nanotube layer onthe surface of the anode material layer is the same as forming the firstcarbon nanotube layer on the cathode material layer. The second carbonnanotube layer can have the same structure as the first carbon nanotubelayer.

The above step S4 can further includes the sub-step of pressing thebattery cell using a laminator.

Referring to FIG. 8, another embodiment of making the lithium ionbattery includes the following steps:

N1: providing a separator having a first surface and a second surfaceopposite the first surface;

N2: applying a cathode material layer on the first surface of theseparator;

N3: forming a first carbon nanotube layer on a surface of the cathodematerial layer to obtain a cathode electrode;

N4: applying an anode material layer on the second surface of theseparator;

N5: forming a second carbon nanotube layer on a surface of the anodematerial layer to obtain an anode electrode; and

N6: encapsulating the cathode electrode and the anode electrode in anexternal encapsulating shell; and

N7: injecting an electrolyte solution into the external encapsulatingshell.

In one embodiment, Step N2 includes the following sub-steps: providingslurry including cathode active material, conductive agent and adhesive;and applying the slurry on the first surface of the separator by acoating method or spinning method. In other embodiments, the method formaking the cathode material layer can be the same as step S1 disclosedabove.

Step N3 is almost the same as step S2 disclosed above. In oneembodiment, after the slurry is applied on the surface of the firstsurface of the separator, the first carbon nanotube layer can be formedon the surface of the cathode material layer after the slurry issolidified or before the slurry is solidified. In one embodiment, thefirst carbon nanotube layer is formed on the surface of the cathodematerial layer before the slurry is solidified, and then the slurry issolidified, so that the first carbon nanotube layer can combine with thecathode material layer tightly.

In one embodiment, Step N4 is almost the same as step N2, but usinganode active material instead of cathode active material. In anotherembodiment, the anode material layer is formed on the second surface ofthe separator by coating slurry including anode active material,conductive agent, and adhesive on the second surface.

Step N5 is almost the same as step N3. The second carbon nanotube layercan have the same structure with the first carbon nanotube layer.

Step N6 is the same as step S5 disclosed above.

Step N7 is the same as step S6 disclosed above.

Finally, it is to be understood that the above-described embodiments areintended to illustrate rather than limit the present disclosure.Variations may be made to the embodiments without departing from thespirit of the present disclosure as claimed. Elements associated withany of the above embodiments are envisioned to be associated with anyother embodiments. The above-described embodiments illustrate the scopeof the present disclosure but do not restrict the scope of the presentdisclosure.

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. The description and the claims drawn to a method may includesome indication in reference to certain steps. However, the indicationused is only to be viewed for identification purposes and not as asuggestion as to an order for the steps.

What is claimed is:
 1. A lithium ion battery comprising at least onebattery cell, the at least one battery cell comprising: a cathodeelectrode; an anode electrode; and a separator sandwiched between thecathode electrode and the anode electrode; wherein at least one of thecathode electrode and the anode electrode comprises a current collector,the current collector is a carbon nanotube layer consisting of aplurality of carbon nanotubes uniformly distributed and substantiallyaligned along a same direction; further comprising a conducting tabelectrically connected to the carbon nanotube layer, and the conductingtab has a strip shape and is substantially perpendicular to the aligneddirection of the plurality of carbon nanotubes.
 2. The lithium ionbattery of claim 1, wherein the carbon nanotube layer comprises aplurality of stacked carbon nanotube films, the plurality of carbonnanotubes in each of the plurality of stacked carbon nanotube films arealigned along the same direction, and the plurality of carbon nanotubesin at least two of the plurality of stacked carbon nanotube films aresubstantially perpendicular to each other.
 3. The lithium ion battery ofclaim 1, wherein the plurality of carbon nanotubes in the carbonnanotube layer are entangled with each other and randomly dispersed. 4.The lithium ion battery of claim 1, wherein the carbon nanotube layercomprises a surface, and an angle between a primary alignment directionof the carbon nanotubes and a surface of the pressed carbon nanotubefilm is greater than 0 degrees and less than 15 degrees.
 5. The lithiumion battery of claim 1, wherein the cathode electrode further comprisesa cathode material layer and the carbon nanotube layer stacked with eachother.
 6. The lithium ion battery of claim 5, wherein the cathodematerial layer consists of a plurality of cathode active materialparticles and a plurality of carbon nanotubes.
 7. The lithium ionbattery of claim 5, wherein the cathode material layer and the carbonnanotube layer are two separate layer structures.
 8. The lithium ionbattery of claim 1, wherein the cathode electrode further comprises twocathode material layers and the carbon nanotube layer, the carbonnanotube layer is sandwiched by the two cathode material layers.
 9. Thelithium ion battery of claim 1, wherein the anode electrode furthercomprises an anode material layer and the carbon nanotube layer stackedwith each other.
 10. The lithium ion battery of claim 9, wherein theanode material layer consists of a plurality of anode active materialparticles and a plurality of carbon nanotubes.
 11. The lithium ionbattery of claim 1, wherein the conducting tab is electrically connectedto the carbon nanotube layer through a point contact.
 12. The lithiumion battery of claim 1, wherein the lithium ion battery comprises aplurality of battery cells stacked with each other.
 13. The lithium ionbattery of claim 12, wherein the cathode electrode comprises cathodematerial layer and the carbon nanotube layer stacked with each other.14. The lithium ion battery of claim 13, wherein the cathode materiallayer consists of a plurality of cathode active material particles and aplurality of carbon nanotubes.
 15. The lithium ion battery of claim 13,wherein the cathode material layer and the carbon nanotube layer are twoseparated layer structures.
 16. The lithium ion battery of claim 12,wherein the cathode electrode comprises two cathode material layer andone carbon nanotube layer, the carbon nanotube layer is sandwiched bythe two cathode material layer.
 17. The lithium ion battery of claim 12,wherein the anode electrode comprises two anode material layer and onecarbon nanotube layer, the carbon nanotube layer is sandwiched betweenthe two anode material layer.
 18. The lithium ion battery of claim 17,wherein the anode material layer consists of a plurality of anode activematerial particles and a plurality of carbon nanotubes.